New Control Over Silicone Synthesis using SiH Chemistry: The Piers–Rubinsztajn Reaction

Abstract

There is a strong imperative to synthesize polymers with highly controlled structures and narrow property ranges. Silicone polymers do not lend themselves to this paradigm because acids or bases lead to siloxane equilibration and loss of structure. By contrast, elegant levels of control are possible when using the Piers-Rubinsztajn reaction and analogues, in which the hydrophobic, strong Lewis acid B(C F ) activates SiH groups, permitting the synthesis of precise siloxanes under mild conditions in high yield; siloxane decomposition processes are slow under these conditions. A broad range of oxygen nucleophiles including alkoxysilanes, silanols, phenols, and aryl alkyl ethers participate in the reaction to create elastomers, foams and green composites, for example, derived from lignin. In addition, the process permits the synthesis of monofunctional dendrons that can be assembled into larger entities including highly branched silicones and dendrimers either using the Piers-Rubinsztajn process alone, or in combination with hydrosilylation or other orthogonal reactions.

Facile Synthesis of Cx(AB)yCx Triblock Silicone Copolymers Utilizing Moisture Mediated Living‐End Chain Extension

“…The PR reaction between SiH groups and a variety of oxygen nucleophiles is known to occur at different rates: alkoxysilanes, phenols > aryl ethers > silanols > water . The utilization of two reactions with SiH groups simultaneously, catalyzed by the same B(C 6 F 5 ) 3 catalyst, allows the controlled synthesis of triblock copolymers.…”

“…Functional silicone precursors bearing SiH and SiOR groups can be sourced from silicone polymers (pendant or telechelic functionality) or from small silanes . In addition to alkoxysilanes, analogous reactions occur with silanols (including mineral surfaces), borates, phenols, and alkyl aryl ethers (Figure B) . Recently, the use of water as a chain extender for α,ω‐hydride‐terminated poly(dimethyl)siloxanes (H‐PDMS‐H) was described.…”

Sequence‐Controlled Catalytic One‐Pot Synthesis of Siloxane Oligomers

“…As stated above, B(C 6 F 5 ) 3 is an excellent catalyst for the dehydrocarbonative cross‐coupling of alkoxysilanes with hydrosilanes (Piers–Rubinsztajn reaction) . The siloxane products obtained by the aforementioned reaction sequence contain ethoxy groups.…”

“…Several types of catalytic cross‐coupling reactions between silanols and halosilanes (Si−OH/X−Si), hydrosilanes (Si−OH/H−Si), vinylsilanes (Si−OH/vinyl–Si), or allylsilanes (Si−OH/allyl–Si), as well as between alkoxysilanes and halosilanes (Si−OR/X−Si) or hydrosilanes (Si−OR/H−Si) have been reported, and these catalytic methods facilitate the selective formation of unsymmetrical siloxane bonds. Among these, the B(C 6 F 5 ) 3 ‐catalyzed dehydrocarbonative cross‐coupling of alkoxysilanes with hydrosilanes, the Piers–Rubinsztajn reaction, offers considerable advantages for the rapid construction of well‐defined siloxanes . For example, Brook and Thompson carefully chose alkoxysilane and hydrosilane building blocks, in terms of their steric demand, and systematically assembled them by using the Piers–Rubinsztajn reaction to obtain branched silicone oligomers in only two steps (Scheme ) .…”

Polysiloxanes Modified by Thiol‐Ene Reaction and Their Interaction with Gold Nanoparticles

“…The functionalization of polysiloxanes is not always easy because the siloxane bond is sensitive to acid or basic conditions. Few reactions are convenient for preserving the silicone polymer and notably the most used is hydrosilylation, but more recently, other strategies are developed such as azide‐alkyne click chemistry, Schiff base chemistry, Piers–Rubinsztajn reaction, thioacetals, aza‐ Michael , etc . The thiol‐ene reaction also appears as a suitable strategy for grafting in a single step various unprotected functional groups, including acids, amines or alcohols.…”